The most trivial form of distance measurement is to measure the period of time it takes for a wave package to travel from a first object to a second and back (signal return time). This allows, on the basis of the usually constant signal travelling speed, to directly deduce the distance. However, due to the high velocity of light and the problems connected to exact time measurement, such method is relatively inaccurate and/or complex.
In view of improving the situation, a distance-measurement method had become known as early as in the middle of last century, which was based on the installation of the Michelson-Interferometer and which works on the basis of phase shift. It is also called Distance Interferometry.
At first, this method certainly is ambiguous, since the distance can only be determined modulo half the wavelength. However, numerous methods are known to remedy that disadvantage, such as from DE 100 38 346 A1 for example. Here, in order to determine the distance, the phase is measured as a basis for calculating the signal return time, which again serves as basis to calculate the distance. The major difference now consists in the fact that the phase allows for a very high resolution, even with simple components, since phase position can usually be determined with an accuracy of few degrees. For wavelengths in the 100 nm to 10 cm range, this leads to resolutions in the nm to mm range.
Thus there are basically two different types of distance measurement methods. Distance measurement by means of phase measurement has been known for a long time different measurement methods developed around the two kinds of distance measurement, which attempt to remedy the respective disadvantages. Concerning the measurement of signal run time reference is made to WO2004/035357, EP 1815267A1, XP 010 136 540 or WO02073562 for example.
Methods which are based on the measurement of phase shift are to be distinguished there from. The present application is concerned with measurement improvement on the basis of the measurement of phase shift. Also on the basis of this principle, special measurement processes have been developed in the attempt of avoiding disadvantages. Thus, for example the low reflected signal intensity or phase jumps which occur in the reflection, constitute problems which can certainly be avoided. This, however, generally leads to a higher complexity of the required circuits, and therefore causes higher costs and a higher susceptibility to environmental influences such as reflections at other objects.
It is known, for example, to use a signal emitted from a first object and reflected at a second object, in order to analyze the phase shift between the emitted and the received signal, in order to determine the distance on that basis.
Furthermore, it is known, to emit a first signal from a first object and to receive it at a second object and to emit a signal from that second object, which signal is generated with a phase in a certain relationship to the wave received at the second object. This second signal is then again received at the first object and is analyzed with reference to the phase difference to the wave emitted at the first object. The result allows for calculation of the distance between the objects.
These methods as described, however, come with numerous disadvantages. For example the use of a signal which was solely reflected on the second object leads to an only very low signal intensity of the reflected wave being available. Further, due to the reflection at different objects, numerous different reflections need to be evaluated.
If a method is used in which a wave is emitted from the second object, the phase of which is in a fixed relationship with the phase of the first wave received on the second object, the problem arises, that reception and emission at the second object are happening simultaneously. This causes numerous problems, since the individual fields overlap, which has a negative influence on the measurement or makes it difficult, if not sometimes even impossible, to separate the individual signals which lie in the same band—that is, with possibly very different levels of intensity (differences of up to 100 db are nothing out of the ordinary). In addition to that, the generation of a wave in phase correlation is relatively complex.
In many applications of phase measurement therefore phase- and/or time-coupled systems are necessary. In a skilled measurement installation, however, this is not necessarily required. Even extremely far de-coupled systems are possible, in which the oscillators are not coupled either, when emitting and receiving. An analysis of the phase angles is nevertheless possible. Such a method is known from EP 2196823, for example.
Another method which is based on the measurement of the phase position, which however always requires a double signal return, because it considers the difference of frequencies and phase angles, in order to avoid problems in the measurement, is known from DE102009060591A1, DE102009060592A1 or DE102009060593A1. By considering the difference, problems which are due to a relative movement, can be avoided. Similar processes are also known from “High Resolution Approach for Phase Based TOF Ranging using Compressive Sampling” by Markus Wehner, Robert Richter, Sven Zeisberg, Oliver Michler, or from IEEE 802.15-09-0613-01-004f by Wolfram Kluge.
Additionally, numerous further methods are known for improving the transmission and measurement. For example, it is known from EP 2259083 A to de-correlate emitted signals in relation to the polarization and/or emission characteristic. This is how it becomes possible, at a receiver, to analyze even in a complex environment the propagation paths or the location of the emitter for example, especially by means of the amplitudes and/or phase positions of the individual wave trains received. If for example an emitter according to the invention is positioned outside a shielded room, and if the shielding of such room has two leaks, such leaks can be located by a correspondingly equipped reception device. When a traditional emitter with no de-correlation is used, this would not be possible, since the signals entering through the leakages would overlap. An analysis of the signal-run times is thus no longer required. This is how numerous problems in the evaluation of distance and/or orientation measurements can be avoided.
From EP 2212705 for example, a method for determining the direction of incidence and other characteristics of a de-correlated wave field is known.
Furthermore, it is also known, from GPS for example, to provide infrastructures which allow the determination of the position also of passive objects. However, systems of such type or respectively infrastructures, come with the disadvantage that either the receivers are complex and expensive, do not work or work only insufficiently within closed buildings, the installation of the infrastructure is complex and costly and/or the position determination is relatively inaccurate.